High emission cathode



Oct. 26,

HIGH EMISSION CATHODE Filed Aug. 14, 1943 INVEN TOR.

BENJAMIN FOX ATTO RNEY.

Patented Oct. 26, 1948 2,452,044 HIGH EMISSION CATHODE Benjamin Fox, New York, N. Y., assignor to the United States of America as represented by the Secretary of War Application August 14, 1943,- Serial No. 498,646

Claims. (01. 250-150) (Granted under the act of March 3, 1883, as

The invention described herein may be manufactured and'used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to electron emission apparatus, and more particularly to electron emitting cathodes therefor.

-The primary object of the present invention is to generally, improve cathodes. A, more particular object of the present invention is to provide a large area cathode, so that a large electron emission is obtained'from a large cathode surface, but the electrons are gathered and used to produce secondary emission in a relatively small region, which region then constitutes a virtual cathode region.

To accomplish the foregoing general object, and other more specific objects which will hereinafter appear, my invention resides in the oathode elements, and other tube elements, and their relation one to the other, as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by a drawing in which Figure 1 is a longitudinal section through a cathode ray tube embodying features of the invention;

Figure 2 is a transverse section taken approximately in the plane of the line 2-2 of Figure 1; and

Fig. 3 is a schematic view of another embodiment of my invention.

Referring to the drawing, the primary or first cathode is a relatively large diameter ring or cylinder l2. A filamentary cathode may be used, but in the present case the cathode is a continuous surface which is preferably oxide-coated on the inside face, and which is indirectly heated, as by means of a heating coil 14. Electrons emitted by the cathode are attracted to and through an accelerating grid l6, and strike a target I8, which acts as a secondary emitter. In the particular case here illustrated, the target is approximately conical in shape. The electrons emitted at l8 may be considered as coming from a second or virtual cathode region of small dimension, compared to the large size of the actual cathode l2.

The electrons are utilized in any desired or conventional manner. In the present case, the

cathode assembly forms a part of a cathode ray tube, and the electrons pass through a focusing electrode 20, and then through one or more control grids 22. 24 may be employed,

Appropriate deflecting electrodes depending on the use to amended April 30, 1928 370 O. G. 757) which the electron beam is tobe put. The elec- 1 trons then strike a screen 26.

. It will be understood that, if desired, a suppressor grid may be disposed about the secondary emitter in order to prevent the emitted electrons from being drawn back to the accelerating grid. Such a structure is shown in Fig. 3, wherein grid 30 is the suppressor grid which is, in accordance usual practice, at cathode potential or-lower. It will also be understood that by applying a sufiiciently .high positive potential to thesecondary emitter, the accelerating grid may be omitted. .It;

will be appreciated that for some purposes a single pair of deflecting plateswill be adequate, in

stead of the two pairs here shown. A magnetic focusing means may be used instead of the electrostatic focusing means illustrated in the drawing. It will also be understood that magnetic deflecting means may be employed, instead of the electrostatic deflecting means shown. Although the grid l6 and target l8 have been referred to as positive, this is meant in a relative sense, for thei electrodes 24 may be at mean ground potentia It should be mentioned that while the cathode assembly has been illustrated as used in a cathode ray tube, it may also be used for an X-ray tube, and also for an ordinary electron emission tube (meaning ordinary in the sense that it is not of the beam type).

It is believed that the construction and operation of my improved cathode assembly, as well as the advantages thereof, will be apparent from the foregoing detailed description. The actual electron emitting surface may be made very large in area, yet the virtual source of electrons is confined to a relatively small region.

It will be apparent that while I have shown and described my invention in a preferred form, many changes and modifications may be made in the structure disclosed, without departing from the spirit of the invention as sought to be defined in the following claims.

I claim:

1. A high emission cathode assembly, said assembly comprising a generally cylindrical cathode of large diameter, a target having an approximately conical surface disposed at the center of said cathode and concentric therewith, and means to polarize the target more positive than the cathode, whereby electrons emitted from the cathode strike said surface and release electrons by secondary emission, the region of said target constituting a Virtual cathode region capable of supply-. ing a relatively large electron current.

3 2.- A high emission cathode assembly, said assembly comprising a generally cylindrical cathode of large diameter, a conical target surface disposed at the center of said cathode and concentric therewith; a cylindrical accelerating *grid disposed i between said-cathode andsaid target, and means to polarize the target more positive than the oathode, whereby electrons emitted from the cathode surface strike said surface and release electrons- "'10 by secondary emission, the region in the vicinity of said target constituting awintual cathodeca pable of supplying a relatively lar g 'ele'ctron"cur rent.

3. A high emission cathode assembly, said assembly comprising a generally cylindrical cathode of large diameter, a target electrode dispos'ed atthe center of said cathode, cylindrical-acceleratelectron stream which comprises the steps of causing .emissionmf'primary electrons from the entire surfa ceenclosing a given space, concentrating said elctr'ons in a region near the center of said space, causing said electrons to produce secondary electrons'in said region, and forming said sec'ondary electrons into a beam directed along the axis of said space.

ing and suppressor grid electrodes disposed-Hoe:

tween said cathode and said targtfand means to so polarize said electrode that electrons emitted fromthe cathodesurfacestrik the "'targtand' release electrons by secondary 'emis s'idnjitliere gior'rbe'twe'en the suppressor gridand said'target constitutin a virtual cathode capable of su ply:

ingarelatiiiely largeelectron current. V

3. A catnbde ray tube-icorn'prising a gras enve': lope; a="cathode"ass'embly' at "one'end of the "enVelopef ail-electronresponsive' elen'intfat the op css ite=endof'th envelope, a recusm -electrod'e diseased-between saidcathode as'semblyarid said eleni'entfsaidcathodeassembly comprising a large hol1ovif-cath=ode; a target disposed-at the =cente'r Number BENJAMIN FOX.

REFERENcEs CITED nae fdllbw'ingrrefrences "ar'fof 'rec'o'rdin'the file'of this'patntf" I UNITED STATES-PATENTS:

W I Name. Date- 1,954,231 Weinberger Apr."10;" 1934-f l,993,fl5'7 Schlesinger Mar."5,1935 2,0QQ',84 Farnsworth t- Novy23fl937 2,131,20 Walds'chrnldt Sept .27,f1938 2,197,033 Diel's"; Apr-."16j-1940" FOREIGN PAI'IENTS Number Country Date 356,978 Great Britamuus Sept. 17,' 1931== 

